<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        p.p1 {
            color: aquamarine;
        }
    </style>
</head>

<body>
    <!-- 标签指定选择器（标签后面直接跟类 --- 不能加逗号和空格） -->
    <p>hello world</p>
    <p class="p1">hello john</p>
    <p class="p1">hello amy</p>
</body>

</html>